The present invention relates to the field of perfumery and the flavourings industry. More particularly, it relates to the use of (6R)-4,5,6,7-tetrahydro-3,6-dimethyl-3H-benzo[b]furan-2-one of the formula 
as a flavouring or perfuming ingredient. The lactone of the formula (I) has excellent organoleptic properties, enabling it to be used to great advantage in perfumery and the flavourings industry.
The present invention also relates to a new process for the preparation of the lactone of the formula (I).
The chemical structure of (6R)-4,5,6,7-tetrahydro-3,6-dimethyl-3H-benzo [b]furan-2-one is known. In fact, K. Schulte-Elte et al in Tetrahedron (1967), 23(6), 2583-2599 identified the compound of the formula (I) in a mixture of lactones resulting from the photooxidation of menthofuran. Furthermore, J. Hirsch et al in J. Org. Chem. (1967), 32(9), 2915-2916 also identified the lactone (I) from among other end products resulting from the hydrolysis of xcex1,xcex1xe2x80x2-dimethoxydihydromenthofuran. However, these authors specify that the lactone (I) oxidises very easily under the synthesis conditions described to give a hydroxylactone, 5,6,7,7a-tetrahydro-7a-hydroxy-3,6-dimethyl-4H-benzo[b]furan-2-one of the formula 
Moreover, some authors such as R. Woodward et al in J. Am. Chem. Soc. (1950), 72, 399-403, who have studied the oxidation of menthofuran by employing greatly varying experimental conditions, have never identified the lactone (I), but have obtained the hydroxylactone (II) as the only oxidation product.
So, although (6R)-4,5,6,7-tetrahydro-3,6-dimethyl-3H-benzo[b]furan-2-one has been detected among other reaction products during the course of studies into the reactivity of menthofuran, no document of the prior art describes optimum synthesis enabling the lactone (I) to be obtained without it oxidising rapidly to form the hydroxylactone (II). In addition, these references give no indication or even a suggestion of the possible use of the lactone (I) as a perfuming or flavouring ingredient.
Moreover, it is important to point out that certain documents of the prior art, which have analysed the constituents of natural products such as the essential oil Pycnanthemum floridanum (C. Shu et al, J. Ess. Oil Res. (1994), 6(5), 529-531) or wild species of peppermint (Nakayama T.; Higashiyama T.; Sakata I.; Hashizume T., Koryo, (1970), 97, 47-56) have identified a product that they refer to as xe2x80x9cmenthofurolactonexe2x80x9d, without specifying its structure. It seems that there is some confusion in the literature with respect to the structure associated with this name: while Chemical Abstracts uses menthofurolactone to refer to the structure (6R)-4,5,6,7-tetrahydro-3,6-dimethyl-3H-benzo[b]furan-2-one, i.e. the lactone (I), documents of the prior art use this name to designate 5,6,7,7a-tetrahydro-7a-hydroxy-3,6-dimethyl-4H-benzo[b]furan-2-one of the formula (II).
For example, Ito et al in Kitami Kogyo Tanki Daigaku, Kenkyu Hokoku (1969), 2(4), 585-587, who describe xe2x80x9cthe isolation of menthofurolactone from Mentha arvensisxe2x80x9d, associate the structure (II) with the name xe2x80x9cmenthofuro-lactonexe2x80x9d and also describe its synthesis by the oxidation of menthofuran. Without doubt, the confusion arises from the fact that, as mentioned hereinabove, both the lactone (I) and the hydroxylactone (II) are products of the oxidation of menthofuran and, according to the prior art, the lactone (I) oxidises very easily to form the hydroxylactone (II). Consequently, the documents of the prior art by C. Shu et al and K. Umemoto, which refer to menthofurolactone as a constituent of a natural product without describing its structure and which date from later than the document by Ito et al referred to hereinabove, do not make it possible to establish what the structure of the lactone detected and named xe2x80x9cmenthofurolactonexe2x80x9d was. On the basis of the experimental conditions employed in the prior art, the compound detected in the natural products is in fact the hydroxylactone of the formula (II). However, we have discovered quite surprisingly that the lactone of the formula (I) is present in the concrete of peppermint in trace form, although this constituent is very difficult to detect. In particular, we were able to ascertain that only certain experimental conditions, with respect to the choice of GC capillary column, allow the detection of the product by gas chromatography coupled with mass spectrometry, GCMS. For example, during GCMS analysis carried out using a polar column of the type used in the documents of the prior art which disclose analyses of natural products, the lactone (I) is not detected. In contrast, the same GCMS analysis carried out over an apolar column enabled us to observe the presence of (6R)-4,5,6,7-tetrahydro-3,6-dimethyl-3H-benzo[b]furan-2-one. It is clearly apparent from this comparison that the two documents referred to hereinabove are using the name xe2x80x9cmenthofuro-lactonexe2x80x9d to designate the hydroxylactone (II).
Therefore, although of known structure, no document of the prior art describes an optimum synthesis of the lactone (I) which would prevent its rapid oxidation into hydroxylactone (II). Moreover, it seems that this lactone has never been identified as a constituent of a natural product. Finally, there is no mention or suggestion in the prior art of the use of (6R)-4,5,6,7-tetrahydro-3,6-dimethyl-3H-benzo[b]furan-2-one as a perfuming or flavouring ingredient.